sync: add thread local storage (TLS) support (#24849)

vlib/sync/tls_default.c.v

@@ -0,0 +1,62 @@
+module sync
+
+// Pthread TLS API functions (via C interface)
+fn C.pthread_key_create(key voidptr, voidptr) int
+fn C.pthread_key_delete(key u64) int
+fn C.pthread_setspecific(key u64, const_ptr voidptr) int
+fn C.pthread_getspecific(key u64) voidptr
+
+// new_tls creates new TLS storage initialized with the given `value`
+pub fn new_tls[T](value T) !ThreadLocalStorage[T] {
+	$if T !in [i8, i16, i32, i64, u8, u16, u32, u64, isize, usize, f32, f64, rune, int, voidptr,
+		$pointer] {
+		return error('new_tls: invalid type ${T.name}')
+	}
+	mut key := u64(0)
+	// Validate key allocation
+	if C.pthread_key_create(voidptr(&key), 0) == 0 {
+		// Initialize storage and verify success
+		if C.pthread_setspecific(key, convert_t_to_voidptr(value)!) == 0 {
+			return ThreadLocalStorage[T]{
+				key:    key
+				in_use: true
+			}
+		} else {
+			return error('new_tls: Failed to initialize TLS value: ${value}')
+		}
+	}
+
+	// Handle allocation failure
+	return error('new_tls: Failed to allocate TLS index')
+}
+
+// set updates the `value` in TLS storage.
+@[inline]
+pub fn (mut t ThreadLocalStorage[T]) set(value T) ! {
+	if t.in_use {
+		if C.pthread_setspecific(t.key, convert_t_to_voidptr(value)!) != 0 {
+			return error('set: Failed to update TLS value: ${value}')
+		}
+	} else {
+		return error('set: TLS storage is already destroyed')
+	}
+}
+
+// get retrieves the current value from TLS storage.
+@[inline]
+pub fn (mut t ThreadLocalStorage[T]) get() !T {
+	if t.in_use {
+		return convert_voidptr_to_t[T](C.pthread_getspecific(t.key))
+	}
+	return error('get: TLS storage is already destroyed')
+}
+
+// destroy releases TLS resources (must be called manually).
+@[inline]
+pub fn (mut t ThreadLocalStorage[T]) destroy() ! {
+	if C.pthread_key_delete(t.key) == 0 {
+		t.in_use = false
+	} else {
+		return error('destroy: Failed to release TLS resources')
+	}
+}